In-plane optical metrology
A structure that is located adjacent to a measurement target on a substrate is used to convert incident radiation from an optical metrology device to be in-plane with the measurement target. The structure may be, e.g., a grating or photonic crystal, and may include a waveguide between the structure and the measurement target. The in-plane light interacts with the measurement target and is reflected back to the structure, which converts the in-plane light to out-of-plane light that is received by the optical metrology device. The optical metrology device then uses the information from the received light to determine one or more desired parameters of the measurement target. Additional structures may be used to receive light that is transmitted through or scattered by the measurement target if desired.
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This application is a continuation application of application Ser. No. 11/835,206, now U.S. Pat. No. 8,068,228, filed Aug. 7, 2007, entitled “In-Plane Optical Metrology”, which is incorporated by reference herein in its entirety.
FIELD OF THE INVENTIONThe present invention is related to optical metrology and, in particular, to metrology in which probe beam is controlled to be in-plane with the measurement target.
BACKGROUNDOptical metrology is commonly employed in process control applications in the semiconductor manufacturing industry due to optical metrology's non-contact and non-destructive nature. Two commonly used optical metrology techniques are reflectometry and ellipsometry.
In optical metrology, a sample is illuminated with broadband or single wavelength light and the light is detected and analyzed after it interacts with the sample.
As semiconductor geometries continue to shrink, increasing demands are placed on the optical metrology techniques. Moreover, the use of non-planar structures, such as FinFET devices, Intel's tri-gate and AMD's multigate device, provides additional challenges to optical metrology, as three-dimensional structural information is difficult to extract.
Accordingly, improved optical metrology devices and methods are desired.
SUMMARYIn accordance with one embodiment, an optical coupler is located adjacent to a measurement target on a substrate. The optical coupler converts incident radiation from an optical metrology device to be in-plane with the measurement target. The optical coupler may be, e.g., a grating or photonic crystal, and may include a waveguide between the optical coupler and the measurement target. The in-plane light interacts with and is reflected back to the optical coupler, which converts the in-plane light to out-of-plane light that is received by the optical metrology device. The optical metrology device then uses the information from the received light to determine one or more desired parameters of the measurement target. Alternatively, an additional optical coupler may be used to receive light that is transmitted through the measurement target if desired.
In accordance with an embodiment of the present invention, a target on a sample is probed using optical metrology with an in-plane radiation, i.e., the radiation incident on the target is parallel to the surface of the sample, which is said to have a 90° angle of incidence.
In another embodiment, an oblique angle of incidence probe beam 112o (illustrated with dotted lines) may be used. The returning beam 116 is converted by the optical coupler 110 to another oblique angle beam 118o (illustrated with dotted lines), which may have the same (or different) magnitude and opposite direction. By way of example, the probe beam 112o may have an incidence angle of 65° and the oblique return beam 118o may have an incidence angle of −65° (although any angle may be used if desired).
While
As illustrated in
The beam reflected by the target 108 is reflected in-plane along beam path 151 back to the optical coupler 110, which converts the reflected beam back to normal. The returning beam passes through the lens 156 and beam splitter 154 and is received by the detector 158. The detector 158 may detect the intensity of the returning beam and may be, e.g., a spectrometer if broadband light is used. In some embodiments, the polarization state of the returning beam may be detected, e.g., with the use of one or more polarizing elements, such as polarizing element 172. The detector 158 is coupled to a processor 160 that can control the operation of the metrology device, along with controlling the positioning of the metrology device with respect to the optical coupler. The processor 160 is a system that includes a computer and a computer-usable medium having computer-readable program code embodied therein for controlling the operation of the metrology device as well as analyzing the data obtained by the metrology system as described herein. The generation of computer-readable program code for controlling the operation of the metrology device and/or analyzing the data obtained by the metrology system is well within the abilities of those skilled in the art in light of the present disclosure. The processor 160 may include a reporting device 162 that reports the results of the measurement. The reporting device 162 may be, e.g., a display, printer, an alarm to indicate when the measurement is out of specification, or memory to store the result of the measurement.
The processor 160 uses the data obtained by the in-plane probe beam to determine the value of the desired parameter of the target 108. The optical response of sub-wavelength scattering can be calculated with known electromagnetic methods, for example, rigorous coupled wave analysis (RCWA) or finite-difference time-domain (FDTD) methods. An empirical or regression analysis may be used to correlate a return signal, such as intensity or polarization, to the change of target process parameters. The correlation may be pre-generated and stored in a library, e.g., in memory 163 in the processor 160 or in other appropriate medium. Alternatively, a correlation formed through regression analysis may be performed in real-time, e.g., by processor 160. The processor 160 may compare the data obtained by the in-plane probe beam to the correlations stored in the library or generated in real-time in order to determine the value of desired parameter.
The reflectometer 150 may include additional elements such as a camera 164 and a flip minor 166 or pin-hole minor 166 that are used to assist in positioning the reflectometer 150 with the optical coupler 110. Additionally, a white light source 168 and beam splitter 170 may be included, e.g., if the light source 152 is a laser. Additionally, one or more polarizing elements 172 may be used with reflectometer if desired.
As illustrated in
As illustrated by dotted lines in
Producing an optical coupler and waveguide is discussed, e.g., in U.S. Pat. No. 7,065,272, and in “An Out-of-Plane Grating Coupler for Efficient Butt-Coupling Between Compact Planar Waveguides and Single-Mode Fibers”, D. Taillaert, et al., IEEE Journal of Quantum Electronics, vol. 38, No. 7, (July 2002), and “A compact two-dimensional grating coupler used as a polarization splitter,” D. Taillaert et al., IEEE Photonics Technol. Lett. 15, 1249-1251 (2003), all of which are incorporated herein by reference in their entirety.
Similarly, the lateral confinement area 456 reflects light that is transmitted through the target 452 back through the target 452 towards the optical coupler 450. Thus, the lateral confinement area 456 allows the optical coupler 450 to operate in both reflection mode, i.e., light reflected directly from the target 452 back to the optical coupler 450, as well as in transmission mode, i.e., light transmitted through target 452 is reflected back through the target 452 to the optical coupler 450.
The vertical and lateral confinement areas 454 and 456 may be produced by materials of high reflectance, such as metals, or alternatively with the use of distributed Bragg reflectors, as schematically illustrated in
In another embodiment, the in-plane metrology using an optical coupler may be performed with optically coupled overlying layers.
As illustrated in
If desired, additional optical couplers may be used, e.g., as illustrated in
A layer of photoresist 604 is spun on or otherwise deposited over layer 602. The photoresist layer 604 is exposed, developed and selectively removed in a conventional manner to form a target area 606 and an optical coupler area 608, resulting in the structure illustrated in
The layer 602 is then etched to form the optical coupler 609 and the target 607 and the photoresist layer 604 is stripped, resulting in the structure illustrated in
If desired, an additional layer may be deposited over the layer 602 and polished back, e.g., through chemical mechanical polishing, to form the optical coupler 609, the target 607 or both. For example, in one embodiment, the target 607 may be protected by a photoresist 610, while an additionally layer 612 is deposited as illustrated in
It should be understood that other process steps may be used to generate an optical coupler along with the target. For example, in another embodiment, the optical coupler and the target are not produced with the same materials.
The exposed material in layer 704 is removed and the remaining photoresist is removed to form the optical coupler 709, as illustrated in
Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. Various adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.
Claims
1. A method of manufacturing an optical coupler on a substrate and adjacent to a measurement target to be measured, the method comprising:
- forming a measurement target on a substrate; and
- forming an optical coupler on the substrate and laterally adjacent to the measurement target, wherein forming the optical coupler comprises producing a series of periodic elements, the optical coupler configured to convert incident radiation that is out-of-plane with the measurement target to be in-plane and directly incident on the measurement target.
2. The method of claim 1, wherein the optical coupler is a grating or a photonic crystal.
3. The method of claim 1, further comprising forming a waveguide between the measurement target and the optical coupler.
4. The method of claim 1, further comprising forming a second optical coupler adjacent to the measurement target, wherein forming the second optical coupler comprises producing a series of periodic elements, the second optical coupler configured to convert radiation after interacting with the measurement target to be out-of-plane with respect to the substrate.
5. The method of claim 4, wherein the measurement target is between the optical coupler and the second optical coupler.
6. The method of claim 1, wherein the measurement target and the optical coupler are formed from the same materials.
7. The method of claim 1, wherein the measurement target and the optical coupler are formed from different materials.
8. The method of claim 1, wherein the substrate is a semiconductor wafer.
9. The method of claim 1, further comprising forming a second optical coupler on the substrate and laterally adjacent to the measurement target, wherein the second optical coupler is configured to convert incident radiation that is out-of-plane with the measurement target to be in-plane and directly incident on the measurement target.
10. A structure comprising:
- a measurement target formed on a substrate along a plane, the measurement target configured to provide information to at least one measurement parameter; and
- an optical coupler on the substrate and located laterally adjacent to the measurement target, the optical coupler comprising a first material and a second material that form a periodic pattern, the periodicity of the periodic pattern configured to convert incident radiation that is out-of-plane with the measurement target to be in-plane with and directly incident on the measurement target.
11. The structure of claim 10, further comprising a second optical coupler comprising the first material and the second material that form a second periodic pattern, the periodicity of the second periodic pattern configured to convert radiation that is in-plane with the measurement target to be out-of-plane with the measurement target.
12. The structure of claim 10, wherein the periodic pattern is a grating.
13. The structure of claim 10, wherein the periodic pattern is a photonic crystal.
14. The structure of claim 10, wherein the first material is the ambient environment.
15. The structure of claim 10, further comprising a waveguide disposed between the optical coupler and the measurement target.
16. The structure of claim 10, wherein the periodicity of the periodic pattern is configured to convert incident radiation with at least one wavelength between 150 nm and 30 μm.
17. The structure of claim 10, wherein the substrate is a semiconductor wafer.
18. The structure of claim 10, further comprising a second optical coupler on the substrate and located laterally adjacent to the measurement target, wherein the second optical coupler is configured to convert incident radiation that is out-of-plane with the measurement target to be in-plane with and directly incident on the measurement target.
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Type: Grant
Filed: Oct 27, 2011
Date of Patent: Jun 11, 2013
Patent Publication Number: 20120039568
Assignee: Nanometrics Incorporated (Milpitas, CA)
Inventor: Ye Feng (Portland, OR)
Primary Examiner: Hoa Pham
Application Number: 13/282,867
International Classification: G01N 21/55 (20060101);